Abr Standard With Vsvd Congestion Control; Optimized Bandwidth Management (Foresight) Congestion Control - Cisco BPX-BXM-155-8DX Installation And Configuration Manual

Chapter 1 The BPX Switch: Functional Overview

ABR Standard with VSVD Congestion Control

The BPX/IGX switch networks provide a choice of two dynamic rate based congestion control methods,
ABR with VSVD and Optimized Bandwidth Management (ForeSight). This section describes Standard
ABR with VSVD.
Note ABR with VSVD is an optional feature that must be purchased and enabled on a single
node for the entire network.
When an ATM connection is configured between BXM cards for Standard ABR with VSVD per ATM
Forum TM 4.0, Resource Management (RM) cells are used to carry congestion control feedback
information back to the connection's source from the connection's destination.
The ABR sources periodically interleave RM cells into the data they are transmitting. These RM cells
are called forward RM cells because they travel in the same direction as the data. At the destination
these cells are turned around and sent back to the source as backward RM cells.
The RM cells contain fields to increase or decrease the rate (the CI and NI fields) or set it at a particular
value (the explicit rate ER field). The intervening switches may adjust these fields according to network
conditions. When the source receives an RM cell, it must adjust its rate in response to the setting of
these fields.
When spare capacity exists with the network, ABR with VSVD permits the extra bandwidth to be
allocated to active virtual circuits.

Optimized Bandwidth Management (ForeSight) Congestion Control

The BPX/IGX switch networks provide a choice of two dynamic rate based congestion control methods,
ABR with VSVD and Cisco's Optimized Bandwidth Management (ForeSight). This section describes
Optimized Bandwidth Management (ForeSight).
Note Optimized Bandwidth Management (ForeSight) is an optional feature that must be
purchased and enabled on a single node for the entire network.
Optimized Bandwidth Management (ForeSight) may be used for congestion control across BPX/IGX
switches for connections that have one or both end points terminating on cards other than BXM. The
ForeSight feature is a dynamic closed-loop, rate-based, congestion management feature that yields
bandwidth savings compared to non-ForeSight equipped trunks when transmitting bursty data across
cell-based networks.
ForeSight permits users to burst above their committed information rate for extended periods of time
when there is unused network bandwidth available. This enables users to maximize the use of network
bandwidth while offering superior congestion avoidance by actively monitoring the state of shared
trunks carrying Frame Relay traffic within the network.
ForeSight monitors each path in the forward direction to detect any point where congestion may occur
and returns the information back to the entry to the network. When spare capacity exists with the
network, ForeSight permits the extra bandwidth to be allocated to active virtual circuits. Each PVC is
treated fairly by allocating the extra bandwidth based on each PVC's committed bandwidth parameter.
Release 9.3.0, Part Number 78-10674-01 Rev. D0, July 2001
Traffic and Congestion Management
Cisco BPX 8600 Series Installation and Configuration
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